Method of preparing alumina gel



April 4, 1950 W. A. FATRlcK JR METHOD OF PREPARING ALUMINA GEL H25 EXHAUST uqum LEVEL 50L msumee T0 ammo Filed Sept. 12,- 1946 ViBRATING SCREEN FOR F\NE ME BUBBLES v lnvmbov. MAf SQ 4. Q/ /Q/av,

Patented Apr. 4, 1950 Walter A. Patrick, In, Mount Washington, "Md., assignor to The "Davison Chemical Corporation,

' Baltimore, Md.

Application September 12,1946, Serial No. 696,595

g Claims. l

invention relates to the preparation of gels having high catalytic and adsorptive proper-- ties and more especialiyto the preparation of aluminum oxide sols and gels from aluminum sul fide. This application is a continuation-impart of my nomncling application Serial No. 447.,4m9, ii ledJune I7, 1942, abandoned.

The properties of aluminum oxide gels have long been recognized and procedures for the prepaeration -:of such :gels have been developed.

Inmany of the prior art processes for the manufacture of aluminum oxide gels extensive washing 01 the gel is required to remove impurities in order that the product will have-the desired propcr tics. This washing step greatly increases the cost of production because of losses in both time and'material.

Other processes have been developed in which sols of oxide are produced directly and which .do not require washing of the gelled product. In these processes, however, it is found tration that it should likewise :be possible to obtain aluminum oxide sols of a somewhat similar concentration.

In some of the processes of preparing aluminum oxide sols directly which .do not necessitate washing of the gel-led product, reaction products are obtained which are undesirable and the disposal of which is .difficult. Also, it is necessary to resort to the use of extraneous materials in some of the processes, which materials are costly and in- 'volve further manipulative procedures for their recovery or separation.

The major object of the present invention is to devise a method of preparing aluminum oxide sols and gels in which sols having .a. high concentration of aluminum oxide may :be directly pre- "pared :a manner which will avoid the disadvantages of the prior art as pointed out hereinbefore.

Another object of this invention is to devise a method of preparing aluminum oxide sols and gels F in which sols having a concentration of 4 to 16% of aluminum oxide may be directly prepared.

A further object of invention is to devise a. method of preparing aluminum oxide gels in which reaction products capable of being easily disposed of are obtained.

Still another object of this invention is to provide a method of producing :gels of aluminum oxide in which sols having a :high aluminum oxide content are prepared by the direct reaction be tween aluminum sulfide and water.

A still further object of this invention is to devise a method of preparing aluminum oxide gels in which sols having a high aluminum oxide content are prepared by reactingifinely divided aluminum :sulfide "with water containing a small amount of a volatile organic acid and in which the hydrogen ion concentration of the reaction mass and the temperature thereof are controlled to produce optimum results.

Among other objects of this invention is an aluminum oxide $01 which in unconcentratedform has an aluminum oxide content of about 4 to 16%.

With these and other objects in view which will appear more fully hereinafter, the invention resides in the product and the method of preparing the same as hereinafter set forth.

In order to more fully illustrate the present invention, there is shown in the single figure of the accompanying drawings a-diagrammatical ar rangement of apparatus suitable for carrying out theyprocess.

In accordance with the present invention, it has been found that by mixing aluminum sulfide (Al-2S3) with water, reaction occurs which results .in the liberation of hydrogen sulfide and the ion-nation of a sol of aluminum oxide. While an exothermic reaction between aluminum sulfide and water will take place under most conditions, when the aluminum sulfide is in ver finely divided form and the water is slightly acidulated with a, weak volatile organic acid such as acetic acid, a rapid reaction takes place liberating the hydrogen sulfide :and forming as a residual prodnot a sol of aluminum oxide.

More particularly, it has been .found in accordwith this invention that a, sol containing a high concentration of aluminum oxide can be obtained by mixing aluminum sulfide (A1283) with 'water, without the necessity of concentrating the sol. During the resulting reaction, hydrogen sulfide is liberated with the formation of a $01 of aluminum oxide. From this sol a suitable gel can be obtained which may be used without washing. A reaction between aluminum sulfide and water will take place under any conditions and very violently if a large quantity of the former is dropped in the latter. When the aluminum sulfide is added slowly and with violent agitation to water slightly acidulated with a weak volatile organic acid such as for instance acetic acid or formic acid, a smooth reaction occurs liberating the hydrogen sulfide and forming as a residual product a sol of aluminum oxide. Upon standing over a. period of time, the length or time depending on the concentration of alumina in the final mix, the sol will set and become a vibrant gel.

The physical character of the hydrogel produced from the hydrosol depends upon a number of factors. For instance, by using varying screen sizes of aluminum sulfide as a starting material, the physical character of the .final gel may be substantially altered. By using an aluminum sulfide of thru a #:60 II. S. standard screen, a dark visibly porous gel is obtained. As the size of the aluminum sulfide is increased to say #30 U. S. standard screen, the gel becomeslighter in color and translucent. The gel'pro-' duced from the latter size is not porous in the sense that pores are visible, but is a smooth material that resembles silica, gel in appearance. The screen sizes mentioned are not intendedas limitation but merely for illustration. sizes of aluminum sulfide will produce gels which are also very satisfactory. I l

' The physical character of the hydrogel depends on the concentration of the alumina. If the concentration is high, say -16% A1203, the gel will be brittle and will break easily. However, on the lower end of the scale, say 3-4% A1203, the gel will be weak and scarcely be strong enough to support its own weight. The tendency is for the'weak' gels to synerese. For example, a 3% alumina'hydrogel on standing for several days gradually assumed the shape of the containing vessel and the liquid of syneresis remained on the surface in the amount of about 5% of the hydrogel volume.

After the reaction between the aluminum sulfide and acid solution is completed, the hydrogen sulfide may be removed by one of two methods. The first is to reduce the pressure above the alumina hydrosol immediately upon completion of the reaction. This may be done in the laboratory by placing the hydrosol in a suction flask, sealing all openings except one which can be attached to a water aspirator. A second Other method of hydrogen sulfide removal is that which is incidental to the drying operation.

After the mixing of the hydrosol, the so] is allowed to set in suitable containers. After it has become hard to such an extent as will permit ease of handling, the gel is removed, broken into fragments if desired and dried. During the drying operation, the gels containing a low percentage' of alumina, less than 7-8% will revert to the hydrosol stage thus permitting the hydrogen sulfide to escape and be collected. However, the i ll diagrammatically an apparatus suitable for carrying out a process embodying the presentinvention. This apparatus comprises a reaction This is caused vesselgenerally indicated by the numeral I p'rovided with a cover member 2. A stirring mechanism 3 is journalled in the cover 2 and extends vertically into the vessel to a point well below the liquid level. The lower extremity of "this stirring mechanism is provided with suitable blades 4 for agitating the liquid and the upper end is connected to a source of power (not shown) for rotating the mechanism. I

A feed conduit 5 for introducing aluminum sulfide into the vessel and a water inlet 6 also project through the cover 2. A vibrating screen 5 may be placed in the feed conduit if the use of aluminum sulfide of fine mesh is contemplated to obtain a sol of the desired characteristics.

A tube 1 of substantial diameter is also car-.

ried by the cover member 2 and depends vertically a substantial distance into the vessel beeath the surface of liquid therein.

haust pipe may include a suitable exhaust pump or equivalent device.

In practice, the vessel I is filled to a predetermined level above the lower end of the tube preparatory to the addition of the aluminum sulfide and the agitator mechanism started. Aluminum sulfide is then added through the feed chute '5 and suificient additional water is con tinuously added to maintain the reaction.

As previously set forth, the particle size of the aluminum sulfide will depend upon the desired characteristics of the end product. If a small particle size is used, a screen is positioned inthe conduit 5.

Preferably, the water is acidulated by the addition of a volatile organic acid such as acetic or formic acid. Sufiicient acid is added to the Water before it is introduced to the vessel to make the water slightly. acid. However, un-

acidulated water can be used if desired.

It has been found that the reaction will proceed satisfactorily within a range above 0 C. and below 80 C. and temperatures within this range do not substantially effect the physical character of the hydrosol. Temperatures in the higher range can be obtained by adding preheated water to the vessel I or using a vessel having a heated jacket. r

The reaction takes place within the cylinder 1 and the resulting release of hydrogen sulfide gas increases the pressure within the cylinder thereby lowering the level of the liquid mixture in the manner indicated in the drawings. This pressure forces the liberated hydrogen sulfide gas through the liquid from which it escapes after passing through the open end of the cylinder I. It then leaves the vessel through the exhaust pipe 9.

As the hydrosol settles to the bottom of the vessel, it is withdrawn through the discharge pipe II). This provides a continuous process.

This product is an aluminum oxide sol having an aluminum oxide content of from 446% which does-not require further concentration. After it is withdrawn from the vessel, it is allowed to set or gel. The so-formed hydrogel may be treated by dehydration to form a highly glassy transparent heat stable gel which has exceedingly fine capillaries therein. As before stated, the residual hydrogen sulfide will escape during the drying operation from hydrogel containing a low percentage of aluminum, less than I8%, before the hydrosol has hardened, thereby reducing the porosity of the final product. In hydrosols containing a higher percentage of aluminum oxide, the hydrogen sulfide escapes after the material has partly gelled, thereby causin the product to be in a more porous or granular state.

The escape of this gaseous by-product makes it unnecessary to wash the aluminum oxide hydrogel. Moreover, because of the highaluminum oxide content of the sol obtained in the outlined "procedure, the time required for the dehydration of the hydrogel produced from the high alumina sol to form the desired gel is materially reduced thereby effecting an obvious economy.

The extremely small amount of acid which is introduced, if an acidulated water is used, into the reaction, is retained'in the sol and is not found to be objectionable. As a matter of fact, it is believed that when acetic or other organic acids are used, the retention of a small amount of the acid in the form of aluminum acetate or similar aluminum compound performs a function in the maintenance of the stability of the material. It should also be noted that the small quantity of acid used does not result in the introduction or objectionable electrolytes into the solution. This is important because aluminum oxide sols are coagulated by electrolytes in solution.

The following examples are given as illustrative of processes embodyin the present invention:

Example 1 The following illustration will serve to demonstrate this invention using acetic acid.

An acetic acid solution was made up which contained 902 mls. of water and 38.4 mls. of glacial acetic acid. An agitator was so arranged as to violently stir the solution while the aluminum sulfide was being added. The aluminum sulfide was ground so that 100% of it would pass through a 100 mesh U. S. screen. A vibrating screen was so arranged that the aluminum sulfide would sift through into the agitated liquid below. One hundred and thirty-five grams of aluminum sulfide was added over a period of two hours which gave a sol containing about 9% A1203. This mix set in a few minutes and upon drying yielded a gel which was porous in structure.

When activated at 825 F. for 1 hour the water vapor adsorption at different relative humiditles at 80 F. were as follows:

At 10% R. H., 9.95% water vapor adsorption At R. H., 13.62% water vapor adsorption At R. H., 19.50% water vapor adsorption At R. H., 28.80% water vapor adsorption At 80% R. H., 53.87% water vapor adsorption At 100% R. H., 57.21% water vapor adsorption Example 2 To illustrate the use of formic acid the following example is given:

Two and six tenths ml. of 90% formic acid was made up with water to a total of four hundred and seventy ml. which corresponds roughly to one half percent solution. To this was added powdered aluminum sulfide in such an amount as to give a calculated 11.5% aluminum oxide in the hydrosol. The aluminum sulfide was added over a period of one and one half hours through a vibrating screen. The resulting hydrosol set and upon drying and activating one hour at 825 F. adsorbed water vapor as follows:

Relative Moisture Humidity at 80 F. P101 UP Per cent Per cent In all of the examples, the procedures were carried out with ingredients initially at room temperature.

In either of the illustrated processes, aluminum 6 will produce an alumina sol, the above-described controls, together with control of the particle size, enable optimum results to be obtained. A washing of the gel produced from the hydrosol of course, unnecessary.

While for purposes of illustrating the invention only one type of apparatus and two detailed processes have been disclosed, it is to be understood that other types of apparatus and processes within the limits set forth in the present specification may be provided by those skilled in the art without departing from the concept of the present invention.

I claim:

1. A method of manufacturing an aluminum oxide sol comprising mixing aluminum sulfide with water at a temperature ranging from about 0 C. to about C., and adding appreciable quantities of a volatile organic acid from the group consisting of acetic acid and formic acid, said acid not exceeding an amount suflicient to form a solution about 1.0 N in acidity.

2. A method of making an aluminum oxide sol comprising mixing aluminum sulfide with water at a temperature ranging from about 0 C. to about 80 C., and adding appreciable quantities of acid to the mixture, said acid concentration in the mixture not exceeding about 1.0 N, said aluminum sulfide and water being mixed in quantities to form a sol of 4% to 16% alumina.

3. A method of making an aluminum oxide gel substantially free of water soluble salts comprising mixing aluminum sulfide with water slightly acidulated with a volatile organic acid from the group consisting of acetic acid and formic acid at a temperature ranging from about 0 C. to about 80 C., removing the hydrogen sulfide formed during the mixing from the mixture, and gelling the sol, said water having an acid concentration not over about 1.0 N.

4. A method of making an aluminum oxide sol Substantially free of water soluble salts comprising mixing aluminum sulfide with water slightly acidulated with acetic acid in the temperature in the range of about 0 C. to about 80 C., said acetic acid concentration in the mixture not exceeding about 1.0 N, said aluminum sulfide and water being mixed in quantities to form a sol of 4% to 16% alumina.

5. A method of making an aluminum oxide sol substantially free of water soluble salts comprising mixing aluminum sulfide with water slightly acidulated with formic acid at a temperature ranging from about 0 C. to about 80 C., said formic acid concentration in the mixture not exceeding about 1.0 N, said aluminum sulfide and water being mixed in quantities to form a sol of 4% to 16% alumina.

WALTER A. PATRICK, J n.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,569,483 Haglund Jan. 12, 1926 1,719,131 Ridgeway et a1. July 2, 1929 1,797,655 Haglund Mar. 24, 1931 1,857,844 Haglund Mar. 10, 1932 1,935,178 Connolly Nov. 14, 1933 OTHER REFERENCES Mellor, Inorg. and Theor. Chem," vol. V, (1924) pp. 282, 330-331. 

3. A METHOD OF MAKING AN ALUMINUM OXIDE GEL SUBSTANTIALLY FREE OF WATER SOLUBLE SALTS COMPRISING MIXING ALUMINUM SULFIDE WITH WATER SLIGHTLY ACIDULATED WITH A VOLATILE ORGANIC ACID FROM THE GROUP CONSISTING OF ACETIC ACID AND FORMIC ACID AT A TEMPERATURE RANGING FROM ABOUT 0*C. TO ABOUT 80*C., REMOVING THE HYDROGEN SULFIDE FORMED DURING THE MIXING FROM THE MIXTURE, AND GELLING THE SOL, SAID WATER HAVING AN ACID CONCENTRATION NOT OVER ABOUT 1.0 N. 